<template>
	<view class="waterfalls-box" :style="{ height: height + 'px' }">
		<!--  #ifdef  MP-WEIXIN -->
		<view
			v-for="(item, index) of list"
			class="waterfalls-list"
			:key="item[idKey]"
			:id="'waterfalls-list-id-' + item[idKey]"
			:ref="'waterfalls-list-id-' + item[idKey]"
			:style="{
				'--offset': offset + 'px',
				'--cols': cols,
				top: allPositionArr[index].top || 0,
				left: allPositionArr[index].left || 0
			}"
			@click="$emit('wapper-lick', item)"
		>
			<image
				class="waterfalls-list-image"
				mode="widthFix"
				:class="{ single }"
				:style="imageStyle"
				:src="item[imageSrcKey] || ' '"
				@load="imageLoadHandle(index)"
				@error="imageLoadHandle(index)"
				@click="$emit('image-click', item)"
			/>
			<slot name="slot{{index}}" />
		</view>
		<!--  #endif -->

		<!--  #ifndef  MP-WEIXIN -->
		<view
			v-for="(item, index) of list"
			class="waterfalls-list"
			:key="item[idKey]"
			:id="'waterfalls-list-id-' + item[idKey]"
			:ref="'waterfalls-list-id-' + item[idKey]"
			:style="{
				'--offset': offset + 'px',
				'--cols': cols,
				...listStyle,
				...(allPositionArr[index] || {})
			}"
			@click="$emit('wapper-lick', item)"
		>
			<image
				class="waterfalls-list-image"
				:class="{ single }"
				mode="widthFix"
				:style="imageStyle"
				:src="item[imageSrcKey] || ' '"
				@load="imageLoadHandle(index)"
				@error="imageLoadHandle(index)"
				@click="$emit('image-click', item)"
			/>
			<slot v-bind="item" />
		</view>
		<!--  #endif -->
	</view>
</template>
<script>
export default {
	props: {
		list: { type: Array, required: true },
		// offset 间距，单位为 px
		offset: { type: Number, default: 10 },
		// 列表渲染的 key 的键名，值必须唯一，默认为 id
		idKey: { type: String, default: 'id' },
		// 图片 src 的键名
		imageSrcKey: { type: String, default: 'image_url' },
		// 列数
		cols: { type: Number, default: 2, validator: num => num >= 2 },
		imageStyle: { type: Object },

		// 是否是单独的渲染图片的样子，只控制图片圆角而已
		single: { type: Boolean, default: false },

		// #ifndef MP-WEIXIN
		listStyle: { type: Object }
		// #endif
	},
	data() {
		return {
			topArr: [], // left, right 多个时依次表示第几列的数据
			allPositionArr: [], // 保存所有的位置信息
			allHeightArr: [], // 保存所有的 height 信息
			height: 0, // 外层包裹高度
			oldNum: 0,
			num: 0
		};
	},
	created() {
		this.refresh();
	},
	methods: {
		imageLoadHandle(index) {
			const id = 'waterfalls-list-id-' + this.list[index][this.idKey],
				query = uni.createSelectorQuery().in(this);
			query
				.select('#' + id)
				.fields({ size: true }, data => {
					this.num++;
					this.$set(this.allHeightArr, index, data.height);
					if (this.num === this.list.length) {
						for (let i = this.oldNum; i < this.num; i++) {
							const getTopArrMsg = () => {
								let arrtmp = [...this.topArr].sort((a, b) => a - b);
								return {
									shorterIndex: this.topArr.indexOf(arrtmp[0]),
									shorterValue: arrtmp[0],
									longerIndex: this.topArr.indexOf(arrtmp[this.cols - 1]),
									longerValue: arrtmp[this.cols - 1]
								};
							};

							const { shorterIndex, shorterValue } = getTopArrMsg();
							const position = {
								top: shorterValue + 'px',
								left: (data.width + this.offset) * shorterIndex + 'px'
							};
							this.$set(this.allPositionArr, i, position);
							this.topArr[shorterIndex] =
								shorterValue + this.allHeightArr[i] + this.offset;
							this.height = getTopArrMsg().longerValue - this.offset;
						}
						this.oldNum = this.num;
						// 完成渲染 emit `image-load` 事件
						this.$emit('image-load');
					}
				})
				.exec();
		},
		refresh() {
			let arr = [];
			for (let i = 0; i < this.cols; i++) {
				arr.push(0);
			}
			this.topArr = arr;
			this.num = 0;
			this.oldNum = 0;
			this.height = 0;
		}
	}
};
</script>
<style lang="scss" scoped>
// 这里可以自行配置
$border-radius: 6px;

.waterfalls-box {
	position: relative;
	width: 100%;
	overflow: hidden;
	.waterfalls-list {
		width: calc((100% - var(--offset) * (var(--cols) - 1)) / var(--cols));
		position: absolute;
		background-color: #fff;
		border-radius: $border-radius;
		// 防止刚开始渲染时堆叠在第一幅图的地方
		left: calc(-50% - var(--offset));
		.waterfalls-list-image {
			width: 100%;
			will-change: transform;
			border-radius: $border-radius $border-radius 0 0;
			display: block;
			&.single {
				border-radius: $border-radius;
			}
		}
	}
}
</style>
